Austria will re-instate border controls with Hungary if Budapest refuses to take in asylum seekers sent to it by other European Union states.

The row between the two EU neighbours has further weakened the already fragile unity in Europe over how to share the burden of a rising tide of migrants.

Several countries on the EU's periphery say the system for tackling migration is broken but Hungarian Prime Minister Viktor Orban's decision to halt transfers of asylum seekers is the most radical step taken by any European leader so far.

Mr Orban has a history of tangling with Brussels, with European Commission President Jean-Claude Juncker, in a barbed joke, once describing him as a "dictator".

Austria itself stopped processing asylum requests this month, in an effort to pressure other EU states to do more to help absorb waves of refugees.

Freedom of movement across internal borders is a fundamental principle of the EU, but hundreds of thousands of non-EU migrants - many trying to head north to countries such as Germany or Sweden - are testing commitment to that ideal.

In Berlin, the head of the Europe department in the Foreign Ministry received Hungary's ambassador to Germany for talks.

The Germans made clear their expectation "that despite the burdens to which Hungary also sees itself exposed in the refugee crisis, responsibilities in the joint European asylum system cannot be unilaterally questioned," a ministry official said.

Foreign Minister Szijjarto said Austria and other EU states were planning to send back to Hungary illegal immigrants who should instead be sent to Greece."We do not agree with this," he told reporters.

He denied his government was violating EU rules.

Conflicts in the Middle East and Africa and a breakdown of order in states along the southern Mediterranean coast have driven the migrants to try to reach Europe.